1. Field of the Invention
The present invention relates generally to a gas turbine engine, and more specifically to a segmented blade outer air seal or BOAS.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
A gas turbine engine includes a turbine with multiple rows or stages of stator vanes and rotor blades. A blade outer air seal (BOAS) forms a gap with tips of the rotor blades. The BOAS is a full 360 degree annular section that is formed from segments. Each BOAS segment includes an inner surface that forms the gap with the blade tips and an outer surface that is covered by an impingement plate with impingement holes formed therein to provide impingement cooling on the outer or backside surface of the BOAS segments. Each BOAS segment has a separate impingement plate typically brazed to the segment. Each BOAS segment also includes forward and aft hooks that are used to secure the segment in place on the turbine casing. Because of thermal growth from engine operation, the BOAS segments are formed with mateface gaps (the gap between adjacent segments) and sealed with a flat seal to prevent hot gas flow up from the inner gas flow path and cooling air flowing into the inner hot gas flow path.
One problem with the prior art segment design is when the impingement plate becomes detached from the segment or has a hole burned through, the cooling air from the cooling air supply cavity above the impingement plate will leak into the mateface gaps and forward and aft hook gaps. Since the impingement plates are also a separate plate, when one becomes loose nothing will hold the plate in place. Also, because of separate impingement plates, brazing or other bonding is required for assembly that also reduces the impingement plate durability because the impingement plate is coupled to the BOAS segment.
Forward and aft retainer rings are also used to provide support surfaces for the BOAS segments. Any gaps formed between the retainer rings and the segments will require a seal to prevent hot gas flow or cooling air leakage.